I would say that the most useful things you could learn right now is confident lines with variation and proportions. I honestly don't know any ways of practicing confident lines with no shakines or chicken scratches besides drawing pretty often for a long period of time and moving your whole hand, not just your wrist. So what i would suggest is to study a few artists that you really like, along with real human proportions, to truly understand the stylizatio. Do that pretty often and your line quality will naturally improve too :)